We propose to develop and evaluate a computer-based intervention using cell phones to enhance adherence to antiretroviral treatment (ART) and support of HIV transmission risk-reduction among adult HIV- positive patients in Peru. Adherence to ART is critical for treatment success at the individual level and to avoid the onset of resistant strains of HIV. In Peru, where ART has recently been introduced, adherence to HIV treatment has not yet beenjaddressed properly. Innovative approaches using information technologies such as cell phones are needed to increase adherence to ART for people with HIV/AIDS. The specific aims of the study are to: 1) Conduct formative research to assess culturally-specific behavioral messages to be included in the computer-based system;2) Develop and test an interactive computer-based system using cell phones to enhance adherence to ART and to deliver HIV transmission risk reduction messages;3) Evaluate the impact of the system on antiretroviral adherence and sexual risk behaviors. To achieve these aims, we will conduct a randomized controlled trial of a 12-month intervention, comparing [1] standard-of- care (n=50) with [2] standard-of-care plus cell phone-based system (n=50) among patients receiving ART at Via Libre, a non-governmental organization established to help people with HIV. We will recruit 100 adults over 18 years old who are currently on ARTs and give consent. The patients will be recruited during a one- year study period and will be randomly assigned to receive either a cell phone-based system or the standard-of-care. Outcomes between the two groups will be monitored using monthly surveys (by phone or the Internet) to determine effects of the intervention on ART adherence and sexual risk behaviors. Self- reported medication adherence and adherence to clinic appointments;and self-reported HIV transmission risk behaviors will be the primary endpoints of interest;impact on HIV-1 viral load and CD4 count also will be assessed. The intervention group will receive: 1) Tailored reminders via their cell phones to take their ART and attend scheduled HIV clinic appointments;and 2) Tailored HIV transmission risk reduction messages via their cell phones. This pilot randomized-controlled trial will define the need and direction for larger evaluations of this cell phone-based system to assess impact on ART adherence and sexual behaviors of vulnerable populations living with HIV in resource-poor settings.